1. Field of the Invention
The present invention relates to liquid crystal electro-optical elements which are used for display devices. More particularly, it relates to a novel twisted effect type liquid crystal electro-optical element (hereinafter referred to as a TN type display element) which comprises nematic liquid crystal material having positive dielectric anisotropy (hereinafter referred to as "N.sub.p liquid crystal") between a pair of electrode plates.
2. Description of the Prior Art
Nematic liquid crystal material (hereinafter referred to as N-liquid crystal) has been used in the past for electro-optical display elements because its optical characteristics are changed by an applied voltage. Heretofore, it has also been known that p-alkylbenzylidene-p'-cyanoanilines having the formula: ##STR1## wherein R is an n-propyl, n-butyl, n-pentyl or n-hexyl group, can be used as an N.sub.p liquid crystal which has an electric dipole moment in parallel to the longer axis of the molecule. Twist-effect type liquid crystal electro-optical elements utilized in the field effect mode, that is, the mode wherein applied voltage causes a change of twist or slant of said N.sub.p - liquid crystal molecules (p-alkylbenzylidine-p'-cyanoanilines), can be actuated by a quite low voltage, such as about 1.5 V for a 10% change of transmittance and about 2 V for a 90% change of transmittance. However, it is most desirable to be able to actuate a TN type display element by an even lower voltage.